Monitoring and surgical removal of epileptogenic brain is indicated for the treatment of many medically refractory focal seizure disorders. Such surgery demands a high degree of accuracy in identifying the epileptogenic foci. Various methods have been used in attempting to determine the location of these foci, and all involve sensing cortical electrical activity using electrical contacts applied in various ways.
While scalp contacts were customarily used for many years to identify epileptogenic foci, accurate localization of the foci was usually very difficult with the recordings obtained from such contacts. Therefore, it has become customary for medical centers to use intracranial recording techniques to better define regions of cortical epileptogenicity whereby the safety and effectiveness of epileptogenic brain monitoring and removal is enhanced.
Intracranial recording techniques have typically involved one of two different types of sensing devices—intracortical depth electrodes or cortical strip/grid electrodes. Depth electrodes are necessary in certain circumstances and applications. Techniques using cortical strip/grid electrodes have been shown to be relatively safe and serve as an alternative to depth electrodes.
Cortical strip/grid electrodes are not invasive of brain tissue. Depth electrodes are narrow, typically cylindrical dielectric structures with contact bands spaced along their lengths. Such electrodes are inserted into the brain in order to establish good electrical contact with different portions within the brain. Cortical strip/grid electrodes, on the other hand, are flat strips that support contacts spaced along their lengths. Such strip/grid electrodes are inserted between the dura and the brain, along the surface of and in contact with the brain, but not within the brain.
Examples of such electrodes include but are not limited to electrodes described in U.S. Pat. No. 4,735,208 (Wyler, et al.), U.S. Pat. No. 4,805,625 (Putz), U.S. Pat. No. 4,903,702 (Putz), U.S. Pat. No. 5,044,368 (Putz), and U.S. Pat. No. 5,097,835 (Putz).
A cortical strip/grid electrode has a flexible dielectric strip within which a plurality of spaced aligned flat contacts and their lead wires are enclosed and supported in place between front and back layers of the material forming the dielectric strip. Each flat contact has a face or main contact surface which is exposed by an opening in the front layer of the dielectric strip. Insulated lead wires, one for each contact, are secured within the strip and exit the strip from a proximal end. The dielectric material used in such cortical strip/grid electrodes is typically a flexible, bio-compatible material such as silicone.
While the “typical” cortical strip/grid electrode works fine in many situations, there are applications for which its structure is not well suited. For instance, it may be desirable to sense and record both cellular activity within the brain with a microelectrode while simultaneously monitoring/recording standard electroencephalography (EEG) activity of the brain with a macroelectrode. Cortical sensing devices that allow sensing elements such as electrical contacts to simultaneously sense/record both cellular and EEG activity in an easy and safe manner would be an improvement over the current state of the art.